Large scale wind turbines in Britain. Without some form of energy storage, the amount of wind power that can be safely and reliability feed into the grid is limited. The author argues that the integration of V2G vehicles offers an appealing pathway to greater use of renewable energy, one that also makes good economic sense.

Putting More Wind on the Wire with V2G

Dr. Willet Kempton developed the concept of V2G (vehicle-to-grid) as a way to leverage the electric utility infrastructure already in place to not only power electric-drive vehicles -- including battery and plug-in hybrids -- but just as critically, to help improve the reliability of the grid. (Be sure to listen to Jasna Tomic's previous presentation on V2G).

While Dr. Kempton notes in his presentation before the California Air Resources Board that the current electric grid is relatively dirty since a large percentage of it relies on coal, the overall system is getting cleaner and the source of the pollution is centrally located. He also points out that there is no need to invest billions in a new infrastructure, unlike hydrogen or other alternative fuels, because electric power is widely available nearly everywhere.

He explains that the amount of wind and solar available in the United States far exceeds the electric power demands of the nation. Wind in particular can be competitive with or cheaper than coal-fired electric power, depending on the location. In this presentation, he cites the example of the Sacramento Municipal Utility District or SMUD that currently buys 39 MW of wind power, but is planning to increase this to more than 200 MW.

"Why is it expanding so fast? Because it is relatively cheap," he stated. The utility is also looking ahead to carbon constraints and concerns over global warming.

SMUD's goal is to have 23 percent of its energy sales generated by renewables by 2011. And while solar power is only about two hours out of phase with peak electric power loads, wind is 12 hours out of phase. Presently, only Jutland in Denmark has experience with such a high percentage of wind power mixed into its grid system. Kempton observed SMUD will be the first U.S. utility to approach what is considered the upper limit of wind power on a grid system. This clearly raises issues of energy storage and 'ramp-up rate', or how quickly other power sources like combined cycle gas turbines and pumped hydro-storage can be brought on line to replace wind as it dies.

Any type of energy storage system will cost money, Kempton acknowledges, but V2G offers one of the lowest cost options because much of the cost is being assumed by the vehicle owner. Also, as Dr. Tomic noted, the kilowatt hour costs of V2G power systems on vehicles are a fraction of the costs of building conventional power plants.

Using SMUD's current customer load as a model, Kempton's "back of the envelope" project, which he considers conservative, a V2G-capable vehicle fleet would have energy storage capacity at any given time equivalent to fifty percent of the utility's load.

He calculated that this hypothetical fleet could power all of SMUD's peak load and hold it there for over an hour.

"That's pretty amazing. Half the vehicles in SMUD's service territory (are V2G). Only half of them are available when you need them. You load is at peak. That's the most load you'll ever have on the hottest day of the summer and every generator fails at once. Lights don't go out, and you can hold it for an hour." By Kempton's estimate this is equivalent to 2000 MW hours of energy parked in just a fraction of the available V2G fleet in the service area.

He further estimates that to handle SMUD's current contracted wind power would require a mix of just over 1,000 V2G vehicles like the AC Propulsion eBox or eDrive plug-in hybrid to provide power "regulation services", which would leave out the fluctuations in wind speed and resulting power. This represents 0.3 percent of the community's vehicle fleet.

To handle the 2011 renewable energy target of 23 percent can be achieved with 2 percent of the fleet being V2G or about 12,000 electric and plug-in hybrids. The "blue sky" -- way to much wind that we can handle -- scenario would require just 7 percent of fleet be V2G-ready.

To absorb all of SMUD's excess overnight wind capacity and discharge it during the day -- solving the 12-hour diurnal storage problem -- would require just 3 percent of the community's vehicles be V2G-capable.

He emphasized that this approach would take huge amount of carbon out of the transportation system, as well as the electric power system. It is even theoretically possible to get as high as sixty percent wind penetration, though getting enough vehicle owners signed up to participate would be a challenge.

"You've got wind power running your vehicle fleet, and you've got this benefit for the electric utility because they can go to much higher penetration levels of wind power than they could otherwise without having to build a whole lot of dedicated storage like pumped hydro, building gas turbines bring in regulation back-up and so forth..."

He pointed out that this offers a viable economic option for utilities and the money not invested in building energy storage systems or back-up power can be used to buy-down the cost differential to the consumer in V2G technology.

"So I pose the question to CARB, 'Do you want the money to be spent on these generation assets that are going to be used to back-up wind or do you want the same amount of dollars spent on electrification of the vehicle fleet?'"

You can listen to Dr. Kempton's presentation in MP3 audio using the players in the right-hand column or by downloading the 7.1MB file to your computer for transfer and playback on your favorite MP3 device. A PDF version of his PowerPoint presentation is available the California Air Resources Board web site.

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